1. Technical Field
The present invention relates generally to compositions used for polishing and planarizing the surfaces of various workpieces, such as the surfaces of semiconductors.
2. Description of the Related Art
Compositions useful for polishing the surfaces of various workpieces are well known in the art. Conventional polishing compositions, which are used for polishing the surfaces of semiconductors, glass, crystal, metal and ceramic workpieces, generally comprise aqueous slurries of an appropriate abrasive agent or particle or mixtures of such particles. Commonly utilized abrasive agents include cerium oxide, aluminum oxide, zirconium oxide, tin oxide, silicon dioxide, titanium oxide, etc. Polishing compositions utilizing such agents are generally used by first applying the composition to a polishing pad or to the surface to be polished. The polishing pad is then applied to the surface, which causes the abrasive particles contained within the composition to mechanically abrade the surface, thus effecting the polishing action. However, such conventional polishing compositions used in the general polishing arts cannot produce the highly specular and planar surfaces required in semiconductor and microelectronic component technology. Moreover, conventional polishing compositions have demonstrated disadvantages, such as poor polishing rates and poor surface quality, in polishing other workpieces. For example, the surfaces of glass, metals and semiconductors polished with such compositions demonstrate various defects such as haze, stains, scratches, undulations, undercuts, mesas, etc.
Attempts have been made in the prior art to improve the existing, commercially useful polishing compositions. Two methods of attaining improvement in these areas include (1) the combination of various abrasives; and (2) adding various adjuvants to the compositions.
Examples of combinations of abrasive particles include combinations of, e.g., cerium oxide and a rare earth pyrosilicate. Examples of the use of adjuvants in polishing compositions include the use of salts such as potassium chloride or ammonium chloride or combinations of such salts to promote the polishing effectiveness of the metal surface by the abrasive agent. However, even the addition of cooperating abrasive agents or the addition of adjuvant materials, has failed to produce completely satisfactory polishing compositions capable of producing the planarized surfaces needed in modern semiconductor and microelectronics technology.
To provide superior results, special chemical mechanical polish (CMP) compositions must be used to polish or planarize the surface of prepared semiconductor workpieces. Such compositions must produce an extremely flat and level surface with a high quality polish, i.e., a planar surface. However, unlike conventional polishing to provide a planar surface, the polishing action must be restricted to the level surface of the workpiece and must not affect the topography, morphology and/or structures below the surface. Only such selective polishing action will produce the desired planar surface. Conventional polishing compositions are not suited for such procedures as they merely produce uneven, undulating surfaces by abrading certain regions on, below and within the surface of the workpiece. It has proven difficult, if not impossible, to use conventional polishing products to obtain smooth defect-free surfaces wherein the polishing composition does not adversely affect the underlying structure of the workpiece.
Even where specially designed CMP compositions are applied as an aqueous slurry to the workpiece, other shortcomings exist such as a high consumption rate of slurry, as well as shortcomings in the delivery of slurry to the center of the semiconductor wafer, via the polishing pad, while polishing the surface of the wafer flat. The polishing pad used also deforms to the surface of the wafer, preventing 100% perfect planarization from being achieved. Another problem with the prior art processes is that the CMP operation upon an oxide has no end point capability and therefore is dependent upon knowing and controlling the removal rate such that the operation can be timed to control the degree of planarization.
Accordingly, it can be seen that a long felt need exists for polishing compositions which provide improved polishing activity at improved rates and which will produce planar and defect-free surfaces, particularly in modern semiconductor and microelectronics applications.